Dual Photo and Thermal Polymerizable Monomers Derived From Methyl Esters of Vegetable Oils

Photo-polymerization or polymerization initiated by light is a facile material synthesis technique used widely in coating, adhesive, lithographic, and dental restorative applications. A wide variety of photo-polymerizable monomers are available that result in a range of polymer properties. Of the monomers available, few are derived from renewable resources. In this study, methyl esters of soybean and linseed oil, produced using standard biodiesel synthetic procedures, were used to synthesize hybrid monomers (i.e., monomers bearing two types of polymerizable functional groups). The methyl esters were amidated with ethanol amine, resulting in α-hydroxy amides of vegetable oil. In one case, the double bonds in the fatty acid residues were epoxidized using H₂O₂ and acetic acid. In another case, the double bonds were not functionalized further. The terminal hydroxyl group was then reacted with an isocyanate acrylate monomer, resulting in acrylated amides of vegetable oil or acrylated epoxidized amides of vegetable oil. Both monomer types were formulated with photo-initiators, and the rapid acrylate photo-polymerization was observed by real-time vibrational spectroscopy. After photopolymerization, the materials were annealed at higher temperatures to promote cross-linking through the epoxide moieties or double bonds in the fatty acid residues by ring-opening or alkyd-type reactions, respectively. The degree of cross-linking for each monomer type was evaluated by measuring the cross-link density of the polymer before and after annealing using dynamic mechanical analysis. The materials developed in this study incorporate approximately 60 wt% renewable materials using green synthetic chemistry and low energy demand processing methods. The high efficiency of monomer and polymer synthesis was accomplished by minimizing solvent use, selecting reactions that proceed to high yields, and utilizing photopolymerization. The polymers prepared have unique properties which allow for simple processing of polymers to complex shapes.